Electrostatic properties of alpha/beta-barrel enzymes were studied by examining the structures of six enzymes containing this fold: triose phosphate isomerase, fructose-1,6-biophosphate aldolase, pyruvate kinase, mandelate racemase, trimethylamine dehydrogenase, glycolate oxidase and of narbonin, a protein with this fold but without any known enzymatic activity. The backbone of the alpha/beta-barrel has a distinct electrostatic field pattern, which contributes substantially to the enzyme's (protein) overall electrostatic fingerprints. When the side-chains are included in the calculations, the electrostatic pattern observed for the backbone is globally conserved and the number of electric field lines per unit surface increases. The electrostatic field calculated in this work are consistent with the known preference of this family of enzymes for negatively charged substrates. The calculations were carried out using the program DelPhi.